Per- and polyfluoroalkyl substances (PFAS) are ubiquitous environmental toxicants that are associated with adverse health outcomes including cancer and thyroid disease. The potential for PFAS exposures to negatively influence human health has generated significant concerns in scientific, governmental and public realms. PFAS are used in numerous consumer products, including nonstick cookware, textiles, and food packaging. Importantly, these chemicals persist in the environment and have long elimination half-lives (~2 to 8 years) in the human body, leading to near-universal exposure (some PFAS have been detected in the serum of more than 99% of the U.S. population). While limited human studies and evidence from animal models implicate PFAS exposures in adverse reproductive and pregnancy outcomes including infertility, pregnancy loss, preterm birth, and low birthweight, knowledge remains scarce, particularly for newer PFAS and PFAS mixtures. Further, studies that examined perinatal outcomes such as preterm birth and low birthweight measured serum/plasma concentrations during pregnancy, which may result in confounding by pregnancy-related physiologic changes. Hence, there is a significant need for studies designed to measure PFAS exposure before conception. To better define the impact of PFAS exposure on reproductive and pregnancy outcomes, and because environmental exposures may also affect male reproductive success, we propose an innovative study to measure serum concentrations of relevant PFAS analytes in both men and women before conception. We will leverage the Environment and Reproductive Health (EARTH) Study (ES009718), a prospective preconception cohort of couples recruited from a fertility clinic and followed through delivery. The aims of this proposal are to determine the extent to which maternal and paternal preconception serum PFAS concentrations (individually and as PFAS mixtures) are associated with: AIM 1) reproductive outcomes of fertilization, implantation, and semen quality parameters; AIM 2) pregnancy outcomes of pregnancy loss and live birth; and AIM 3) birth outcomes of birthweight and gestational age. Innovations include the assessment preconception exposure to emerging and new PFAS and their mixtures in couples and the investigation of early reproductive and pregnancy outcomes that have not been previously studied. The proposed study is highly time- and cost-efficient, as we will have archived biospecimens and clinical data available for 834 nulliparous women and 435 men (435 couples). We will recruit an additional 225 nulliparous women and 180 male partners to increase statistical power to a total of 615 couples. Our team includes expertise in male and female reproductive and environmental epidemiology, PFAS exposure assessment, and advanced biostatistical and mixtures analysis methods. The proposed study will have important scientific and public health implications by examining both maternal and paternal PFAS exposure on reproductive, pregnancy, and birth outcomes, providing much needed data for evidence-based policy to reduce PFAS exposure and harm.